Polyamines, abundant and ubiquitous components of the diet, are highly mutagenic when reacted with nitrite, a food additive and also a normal component of the diet (Kokatnur et al., 1978). Nitrous acid mutagenesis has been the subject of investigation for over 20 years. Recent observations have called into question the commonly accepted conclusion that base substitutions induced by nitrous acid are due to mispairing of deaminated bases. The probable involvement of alkylation by nitrosated polyamines and of error-prone repair, rather than mispairing of deaminated bases, in the induction of base substitution mutations by nitrous acid will be investigated. The possibility that the mutagenic action of nitrous acid is a consequence of reaction with endogenous amines will be investigated by extraction of the prospective mutagens from cells which have been treated with nitrous acid. Nitrite-polyamine reaction products will be: 1) tested for their action on prokaryotic and eukaryotic cells with repair and/or replication related defects; 2) tested for their action on specific repair and/or replication related enzymatic reactions; 3) examined for in vivo alkylation reactions specifically associated with the replication fork; 4) examined for the induction of inter- and intra-strand crosslinks in DNA.